The present invention relates to a single- or multi-component injection molding machine with a nozzle-side clamping plate firmly connected to a machine bed as well as a closing-side clamping plate which is movable relative to the nozzle-side clamping plate, wherein both clamping plates carry each a mold half of an injection-molding tool and wherein at the nozzle-side one or several injection units are provided for supplying one or more thermoplastics to the nozzles.
For a better understanding of the object on which the present invention is based, such an injection-molding machine is explained below on the basis of an example of a two-component injection-molding machine with reference to FIGS. 1 to 5.
FIG. 1 is a schematic representation of a two-component injection molding machine according to the state of the art. The injection-molding machine 1 comprises a stationary machine bed 2 with a support plate 3 firmly connected thereto. The functions of an injection-molding machine as described below can be realized with a machine, which does or does not include guide bars.
On the machine bed 2, a closing unit for an injection molding tool is disposed. Shown is a two-component tool, which operates according to the principle of an indexing turntable 7a. 
When, below, an operating piston 5 is referred to, it is to be understood that a drive mechanism is meant, which comprises a bell crank and/or a closing cylinder.
The closing unit comprises a movable clamping plate 4, which is slidable on the machine bed 2 by the operating piston 5 in the direction of the arrow a. The clamping plate 4 is defined as so-called “closing-side clamping plate”. On the movable closing-side clamping plate 4 a first ejector-side mold half 6 of an injection molding tool with a first mold nest (7a and 7b) is disposed. This mold nest consists of a rotatable indexing plate 7a and a mold insert 7b. Opposite the closing-side clamping plate 4, a nozzle-side clamping plate 8 is disposed which is firmly connected to the machine bed 2. By this clamping plate 8, the so-called nozzle-side is defined. On the nozzle-side clamping plate 8, the second mold half of the injection molding tool 9 is disposed which, again, includes a second mold nest (not shown), which is complementary to the first mold nest 7. At the backside of the nozzle-side clamping plate 8, two injection units 10, 11 are disposed.
Upon closing the two mold halves 6 and 9, the operating piston 5 biases the closing-side clamping plate 4 against the stationary nozzle-side clamping plate 8. In this way, the two mold halves 6 and 9 are engaged with each other. In the interior thereof cavities are formed by the first mold nest 7a, 7b and the second mold nest, which is complementary thereto. With the two-component injection molding machine shown in FIG. 1, an upper cavity 13 is formed which is in communication with the upper injection molding unit 10 and a lower cavity, which is in communication with the lower injection molding unit 11. With the two injection molding units 10, 11, two different and/or the same plasticized thermoplastics can be injected into the upper and the lower cavity 13, 12. The first thermoplastic may be for example a thermoplastic material, which is relatively hard after hardening and onto which, for example, a relatively soft sealing lip is injection molded using the second thermoplastic; or the first thermoplastic is transparent and the second thermoplastic is opaque.
During the manufacture of so-called two component injection molding parts with the injection molding machine shown in FIG. 1, it is desirable during mass production that a second thermoplastic, which is introduced by way of the upper injection-molding unit 10, is attached, for example, to a first thermoplastic which has been introduced into the lower cavity 12 by way of the lower injection molding unit 11.
For this purpose, different methods are known for bringing an unfinished injection molded body, which has been formed in the lower mold cavity 12 from the first thermoplastic, into the operating range of the upper injection molding unit 10 to provide there for the attachment, by injection-molding, of the second thermoplastic. To this end, it is known to utilize, at the ejection-side mold half, a rotating structure, which will be described in greater detail below, and which is mounted to the front side of the clamping plate 4. The two-component injection molding method will be described in detail further below.
FIG. 2 shows, different from FIG. 1, the section of an injection molding machine 1 with bars 14 in a view, which is detailed with respect to FIG. 1. Shown is a closing unit to be inserted into an injection-molding machine in a perspective exploded view. With the different kind of representation of FIG. 1 and FIG. 2, it is intended to be indicated that there are different types of machines in the injection molding field.
The movable closing side clamping plate 4 is guided at its four corners by guide bars 14. The guide bars 14 extend into each corner between the support plate 3 shown in FIG. 1 and the nozzle-side stationary clamping plate 8. The clamping plate 4 is movable along the bars 14 in the direction of the arrow a by an operating piston 5 (not shown in FIGS. 2 and 3). In addition, the clamping plate 4 has a central opening 15, through which linear motion transmission elements, which are connected to an ejection unit, (not shown in FIGS. 2 and 3) can act on a stud 16 or a rotatable shaft 25 (FIG. 4), which is disposed at the rear end of a closing side tool engagement plate 17 of the molding tool in front of the closing-side clamping plate 4. By way of the stud 16 or the rotatable shaft 25, the sliding movement of the ejection unit (not shown) can be transmitted to the ejector pins (see FIGS. 4 and 5, reference numeral 28) in order to eject finished injection-molded pieces out of the closing-side mold half 6. In FIG. 2 the closing-side mold half is in the form of a sandwich structure, which comprises the tool engagement plate 17, support webs 18 disposed thereon and a closing-side molding plate 19 disposed on the support webs.
The ejection pins are disposed between the closing-side tool engagement plate 17, the support webs 18 and the closing-side mold plate 19. The closing-side mold nest 7 shown in FIG. 1 consisting of a rotating indexing plate 7a and the mold insert 7a is integrated into the mold plate 19.
During movement of the closing unit into a closed position, the closing-side clamping plate 4, together with the tool engagement plate 17, the support webs 18 and the closing-side mold plate 19 disposed on the closing-side clamping plate 4 are pressed onto the nozzle-side mold half 9, which consists of a nozzle-side molding plate 20 and a nozzle-side tool engagement plate 21. In this way, the two molding plates 19, 20 are placed on top of each other along the separation plane W shown in FIG. 3 and define in their interior the injection-molding cavities.
In connection with two-component injection molding procedures, it is known in practice to remove an unfinished injection molded body formed in the first cavity from the first cavity upon retraction of the closing side clamping plate and place it—using a robotic arm—into the second cavity 13. Upon closing the clamping plate 4 again, the second thermoplastic material component is then injected into the second cavity 13 to be added to the unfinished injection molded body. At the same time, a new unfinished injection molding body of the first thermoplastic material can be formed in the first cavity 13 from which the unfinished injection molded body has been removed by the robotic arm. However, as a result of the transfer of the unfinished molded body by a robotic arm, the effective cycle times are relative long with this procedure and, furthermore, an expensive robotic mechanism is required.
It is also known from the state of the art to engage the closing-side mold half 6 not directly with the closing-side clamping plate 4, but rather to mount it on a so-called turntable 23 (FIG. 4). Upon movement of the clamping plate 4 onto the nozzle-side clamping plate 8, a first cavity is formed for example by the lower closing-side mold nest and the lower nozzle-side mold nest, into which the first thermoplastic material is injected. Upon opening of the closing-side clamping plate 4, the unfinished injection molded body remains in this case in the closing-side lower mold nest.
The turntable 23, which is generally operated by a toothed rod and a gear cooperating therewith or by a motor and a gear is rotated upon retraction of the clamping plate 4 together with the mold half 6 disposed on the turntable 23 by 180°. After the tool has again been closed, the previously lower (now upper) closing-side mold nest and the upper nozzle-side mold nest form a second cavity, in which the unfinished injection molded body is embedded. Now the second thermoplastic material is injected and is attached to the unfinished molded body. At the same time, the previously upper (now lower) closing-side mold nest and the lower nozzle-side mold nest form a first cavity into which first thermoplastic material is injected to form another unfinished molded body during the same time in which the first unfinished molded body is completed in the upper cavity.
When the closing-side clamping plate 4 is again retracted the completed injection molded body is removed from the upper cavity and the turntable 23 with the second injection molded unfinished body embedded in the lower mold nest is again turned by 180° so that the cycle starts anew.
Although the use of a turntable 23 as described above has the advantage that the effective cycle times are noticeably reduced when compared with the use of a robotic arm removal technique, a problem remains in that the turntable 23 has to be driven by an external drive mechanism (hydraulic piston linkage or a mechanism with a gear and a toothed rod or an electric motor). As a result, the arrangement is relatively large and heavy so that relatively long periods are required for a conversion upon disassembly or the exchange of a turntable 23.
Also, the opening stroke of the molding tool is substantially reduced because of the large installation depth of the rotating unit between the two clamping plates. This often requires the use of a larger and therefore less economical injection-molding machine as it would be necessary based on the size of the injection-molded body.
FIG. 4 is a cross-sectional view of such a known rotating unit. A closing-side clamping plate 4, which is movably supported on a machine bed is provided with a central opening 15. On the closing side clamping plate 4, a rotatable unit 22 is disposed. The rotatable unit 22 comprises a turntable 23, which is connected to the clamping plate 4 and a gear 24 mounted centrally on the turntable 23.
A tool support plate 17 is disposed on the rotatable unit 22. Support webs 18 are disposed on the support plate 17. In the mold plate 19 which is supported by the support webs, the lower as well as the upper cavities 12 and 13 are provided into which the ejector pins 28 extent from the backside thereof.
In this embodiment, the rotatable shaft 25 is axially movable relative to the gear 24 in the direction of the arrow a. This axial movement of the rotatable shaft 25 is achieved by a cylinder drive (not shown). The rotatable shaft 25 is provided along its length with a multi-groove profile, which transmits the angular positions of the gear 24 to the rotatable shaft 25. The drive of the gear 24 in the turntable 23 is always a direct drive. When the two mold halves are engaged with each other, the rotatable shaft 25 is moved axially out of the mold nest 7 and the rotatable indexing plate 7a is turned by 180°.
If, for certain applications, the maximum travel distance x (FIG. 1) is to be utilized the turntable 23 has to be removed from the arrangement as shown in FIGS. 4 and 5. Depending on the size and the dimensions of the toothed rod 26 and the hydraulic cylinder 27, this may require extensive conversion efforts. The expensive internal support in the rotatable plate makes it also susceptible to servicing. It is particularly noteworthy that, in turntable drives with external hydraulic connections, also leaking problems occur frequently.
It is the object of the present invention to overcome the disadvantages of the state of the art explained in connection with the description of FIGS. 4 and 5.
In accordance with the invention, this is solved by the measures of claim 1.
The dependent claims relate to preferred embodiments of the present invention.
The advantages and features of the present invention are apparent from the following description of embodiments in connection with the drawings.